1. Field of the Invention
The present invention relates to a substrate transfer apparatus for removing a substrate from, or accommodating or placing a substrate in a substrate accommodating tray, a method for removing the substrate from the substrate accommodating tray using the substrate transfer apparatus, and a method for accommodating the substrate in the substrate accommodating tray using the substrate transfer apparatus. The substrate is used for producing a display panel of, for example, a liquid crystal display device.
2. Description of the Related Art
A display panel for a liquid crystal display device usually includes a pair of display glass substrates opposed to each other and sealed together, and a liquid crystal material sealed between the pair of glass substrates. In order to produce such a display panel, glass substrates are transported to a display panel production plant. For transporting the glass substrates, a glass substrate accommodating box for accommodating a plurality of glass substrates is usually used. Glass substrates are used in display panels of various types of display devices as well as liquid crystal display devices. The above-mentioned type of glass substrate accommodating box is also used for transporting glass substrates used for the various types of display devices other than liquid crystal display devices.
The same type of glass substrate accommodating box is used for transporting glass substrates having electrodes and the like formed thereon as half-finished products, which will be used for producing display panels.
Recently, glass substrates having a thickness of 0.7 mm or less are widely used for various types of display panels. As the glass substrates are increasing in size, the planar area of the glass substrates which are carried to the display panel production plants is increasing, and even glass substrates having a side length of 1.3 m or greater are used.
Such a large and thin glass substrate easily warps. When a plurality of such glass substrates are vertically accommodated in the box with an interval, the glass substrates may warp and contact each other and break during transportation. In order to avoid this, it is necessary to keep an appropriate distance between the glass substrates in the box.
For example, a glass substrate having a thickness of 0.7 mm and a side length of 1.3 m or greater, when supported along the periphery thereof with a support having a width of 20 to 30 mm in a vertical state may warp by 90 mm or greater at the center thereof. In a glass substrate accommodating box, it is necessary to keep a distance of 100 mm or greater between the glass substrates in the box. This inevitably increases the size of the glass accommodating box.
A glass substrate is removed from a glass substrate accommodating box using, for example, a glass substrate adsorption hand as disclosed in Japanese Laid-Open Publication No. 2001-93969. The glass substrate adsorption hand has a pair of flat adsorption pads. Each adsorption pad needs to be inserted between two adjacent glass substrates, which requires a space for inserting the adsorption pad. A flat adsorption pad usually has a thickness of about 20 mm. Therefore, the distance between the glass substrates in the box needs to be the sum of a distance sufficient for preventing the glass substrates from contacting each other even when the glass substrates warp and a distance of about 20 mm for inserting the adsorption pad. This also inevitably increases the size of the glass accommodating box.
Due to the necessary space between two adjacent glass substrates, the number of glass substrates which can be accommodated in a glass substrate accommodating box having a prescribed size is limited. This lowers the space efficiency for transportation and storage, i.e., the number of glass substrates which can be accommodated per unit volume.
In order to solve these problems, Japanese Laid-Open Publication No. 10-287382 discloses a substrate tray cassette for accommodating one glass substrate. A substrate accommodating section of the substrate tray cassette has a lattice structure. The substrate tray cassette is structured such that a plurality of substrate tray cassettes can be stacked vertically. Such a substrate tray cassette allows a large and thin glass substrate to be accommodated without warping and thus without being broken during transportation. Since a greater number of substrate tray cassettes can be stacked vertically for transportation and storage, the space efficiency can be improved.
However, this substrate tray cassette has the following problems. The accommodated glass substrate is supported by resin pins, and a pair of adsorption pads of a glass substrate adsorption hand are put into the space below the glass substrate which is supported by the resin pins. Such a space for the adsorption pads increases the size of the substrate tray cassette.
In order to remove the glass substrate accommodated in the substrate tray cassette using an adsorption hand, it is necessary to separate the plurality of substrate tray cassettes stacked vertically one by one so as to make a large space above the accommodated glass substrate. Accordingly, in order to automatically remove the glass substrate from each of the substrate tray cassettes stacked vertically, a large and complicated apparatus is required.
In order to remove the glass substrate from each of the plurality of substrate tray cassettes stacked vertically and then stack the substrate tray cassettes vertically after the glass substrates are removed from the substrate tray cassettes, a large work space is required and it is impossible to work efficiently.